Total Uptake and Incorporation into DNA of3H-Thymidine,3H-Deoxyuridine and3H-Thymine in the Primary Root ofVicia fabaL.

Abstract

Total uptake of 3H-thymidine, 3H-thymine, and 3H-deoxyuridine and incorporation of these substances into DNA have been investigated in excised roots in Vicia faba. Total uptake was found to be higher in excised roots than in intact ones. This was a consequence of exogenous 3H-DNA precursors entering the excised roots through the cut surface. Where the cut surface was not immersed in the 3H-thymidine solution 3H uptake was also higher than in intact roots. In this case 3H uptake seemed to be correlated with water-loss from the cut surface. Incorporation of 3H-thymidine, 3H-thymine, and 3H-deoxyuridine into DNA was found to be higher in excised roots than in intact ones, probably as a result of a decrease in the size of the relevant endogenous precursor pools. It is suggested that this decrease resulted from the cessation of the supply of DNA precursors to these roots from the cotyledons.